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JOURNAL 0s CHEMICAL EDUCATION
FEBRUARY. 1927
THE STRUCTURE OF MATTER: A BRIEF REVIEW OF PRESENTDAY CONCEPTIONS
V. UP-TO-DATE CHEMISTRY IN THE GENERAL CHEMISTRY COURSE MAURICE L. HUGDINS, S T A ~ OUNIVERSITY, RD CAL~PORNIA
How Much? Opinions will, of course, differ very widely as to how much of the material outlined in the preceding papers of this series should be taught in a general chemistry course in high school or college, also as to how and when it should be taught. All the writer can do is to give his own ideas about these matters, offering them as suggestions to others having this problem to face. The importance of a knowledge of this material-because of its value in systematizing and explaining old facts and in predicting new facts and suggesting new experiments-cannot be questioned, especially as much of the chemistry of the future--for which we should prepare our studentsis sure to be intimately connected with these developments of the past few years. Most important of all, perhaps, is the interest-arousing power of the subjects. The student is sure to be more interested in chemistry if he can see just what advances chemists have made in the past few years toward answering his "what" and "why" questions and if he is given hints now and then as to problems still awaiting solution than if he is taught chemistry as though it were a dead language. For such reasons, the writer believes in including a large percentage of the subject-matter dealt with in these papers in a course in general chemistry-especially in a college course. What?
In a high-school course, it would seem to be important to define and explain rather carefully such terms as proton, electron, nucleus, element, isotope, kernel, valence electron, atom, ion, molecule, and polarity. The relationships between these entities and a simplified periodic table should be discussed. The tendencies of valence electrons to form pairs and octets and the methods by which these tendencies are satisfied should be emphasized-the student should have as clear an idea as possible of the nature of chemical combination. The Bobr theory should be mentioned, for the student should realize that the electrons are probably not in fixed positions, although for chemical purposes we treat them as if they were. The regularity characteristic of crystals and the irregularity characteristic of a m ~ r ~ h o n s ~ s o land i d s liquids should be pointed out. Simple
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crystal structures, such as hose of C, ZnS, NaC1, Cap2, As, HgI,, Se, SnIa, and the "close-packed metals might profitably be described and explained in terms of the structures of the component atoms. When organic chemistry is under discussion, the nature of double and triple bonds should, of course, be mentioned. In a college course the same ground ought to be covered, but in more detail, especially the consideration of the relationships between the periodic system and structure and the study of crystal structures. All of the type structures mentioned in the fourth article of this series might well be taken up. Secondary valence should be considered in some detail and residual affinity mentioned. The simple Bohr theow might be discussed, but it should not be emphasized. When? The writer believes that the sooner the fundamental ideas of atomic and molecular structure are introduced to the student the better. He should be taught early to think in terms of atoms, molecules, and electrons and to relate likenesses in properties to structural similarities and to periodic system relationships. These relationships should be stressed throughout the course; they serve to correlate and explain a large number of otherwise unrelated and unaccounted for facts. The study of crystal structures can conveniently be introduced when the nature of solids is first taken up. Particular structures can be considered later as various elements and compounds are mentioned. A discussion of secondary valence would seem to be most appropriate in connection with the study of complex ions. The new material should not, in the writer's opinion, be taught as a separate subject, but should be impregnated into the course in such a way as to make the point of view throughout an up-to-date one.
How? It is up to each individual teacher to determine just how to revise his course so as to include this new material. Methods must vary with the teacher, the text-book, and the available equipment. The author recommends the liberal use of models, diagrams, and problems. A set of modelbuilding apparatus should prove very useful, both for lectures and in the laboratory.' 1 The writer has found one-inch cubes of maple, having hales bored in each comer and the center of each face and used with 'I8' aluminum rod n ~ to t appropriate lengths, very satisfactory. Solid rubber balls, one inch in diameter, which can be bought for a cent apiece, are also very useful. Holes can be made in them very easily by means of a hot awl or nail.
The teacher should, throughout the course, instill interest by reference to unsolved problems and unproved theories, but in so doing he should religiously diierentiate between fact, theory, and speculation, and try to train his students to do the same.
